1. Field of the Invention
The present invention relates to a method of forming a metal coating and particularly to a method of forming a metal coating capable of suitably forming a metal coating using a solid electrolyte membrane.
2. Description of Related Art
When an electronic circuit substrate or the like is manufactured, a metal coating is formed on a surface of the substrate so as to form a metal circuit pattern thereon. For example, as a technique of forming such a metal coating, a technique (Japanese Patent Application Publication No. 2010-037622 (JP 2010-037622 A)) of forming a metal coating on a surface of a semiconductor substrate of Si or the like by plating such as electroless plating; and a technique of forming a metal coating using a PVD method such as sputtering are disclosed.
However, when plating such as electroless plating is performed, a washing process is necessary after the plating, and a process of treating a waste liquid used during the washing process is also necessary. In addition, when a metal coating is formed on a surface of a substrate using a PVD method such as sputtering, internal stress is generated in the formed metal coating. Therefore, the PVD method has a limit in increasing the thickness of a metal coating, and particularly in the case of sputtering, a metal coating can be formed only in a high vacuum environment.
From this point of view, for example, a coating forming device 6 illustrated in FIG. 10A is disclosed, the coating forming device 6 including at least: an anode 61 that is formed of a porous body; a solid electrolyte membrane 63 that is disposed between the anode 61 and a substrate B, which forms a cathode, such that a solution L containing metal ions is in contact with a portion of the solid electrolyte membrane 63 on the anode 61 side; and a power supply 64 that applies a voltage between the anode 61 and the substrate B (for example, JP 2010-037622 A). Here, in a housing 65 of the coating forming device 6, a storage 69 in which the solution L containing the metal ions is stored is formed, and the anode 61 and the solid electrolyte membrane 63 are disposed such that the solution L containing the metal ions in the storage 69 can be supplied to the solid electrolyte membrane 63 through the anode 61.
Using this coating forming device 6, the power supply 64 applies a voltage between the anode 61 and the substrate B, and metal is deposited on a surface of the substrate B from the metal ions contained in the solid electrolyte membrane 63. As a result, a metal coating F formed of the metal is formed on the surface of the substrate B.
When the device illustrated in FIG. 10A is used, the size and shape of the anode 61 are set according to a coating-forming region (deposition range) of the substrate B. However, as illustrated in FIG. 10B, the metal ions in the solid electrolyte membrane 63 are radially diffused in a width direction of the solid electrolyte membrane 63 as well as a thickness direction thereof.
At this time, during coating formation, a portion of the metal ions diffused to the outside of an edge 61a of the anode 61 (specifically, the metal ions diffused in a direction S2 of FIG. 10B) is returned to and deposited on the coating-forming region along with movement of an electrical charge in the thickness direction (direction S1 of FIG. 10B) of the solid electrolyte membrane 63.
However, the remaining portion of the metal ions may be deposited on a non-coating-forming region (non-deposition region) on which the formation of a metal coating is not desirable. As a result, a metal coating having a desired pattern shape may not be formed. Further, when metal is deposited on the non-coating-forming region, an electric charge which is supposed to be consumed in the coating-forming region is consumed in the non-coating-forming region, which may lead to a decrease in the coating-forming rate.
From this point of view, a technique of masking a non-coating-forming region of the substrate B, which is generally to be subjected to wet plating, with a masking material 40 as illustrated in FIG. 10C is also considered one of the countermeasures against the decrease in the coating-forming rate.
However, the masking material 40 is thick, and thus when the solid electrolyte membrane 63 is brought into contact with the substrate B using a device illustrated in FIG. 10C, a portion of the coating-forming region near an edge D is in the non-contact state. Accordingly, metal is not deposited on the edge of the coating-forming region which is in the non-contact state. As a result, a metal coating having a desired pattern shape may not be formed.